An examination method of this kind can, for example, be used when performing digital subtraction angiography (DSA) and is known from U.S. Pat. No. 7,500,784 B2 which is explained below with reference to FIG. 6.
The quantification of blood flow on the basis of image data during an intervention is a clinically relevant problem. For example, the measurement of blood flow rates in a blood vessel (for example expressed in ml/min) on the basis of X-ray images could be used to evaluate interventional treatment of stenoses for example in cerebral or in peripheral vessels in the catheter laboratory and hence to provide the doctor with information on the outcome of the therapy. Therefore, the doctor could, for example, determine whether the reopening of an occluded vessel by means of a balloon or the implantation of a stent has resulted in an increase in the blood-flow rate to the desired degree.
Invasive possibilities for the measurement of blood flow already exist and are already in clinical use. One example of a method is the use of thermodilution catheters, which are introduced into the blood vessel to be examined. During thermodilution, a specific volume of a cooled solution is injected intravenously. The cold liquid passes through the right half of the heart, then the lung and the left half of the heart, following which it enters the systemic circulation. At a measuring point, the temperature of the blood is determined and a so-called thermodilution curve recorded. However, in terms of the workflow, this technology is complicated, expensive, relatively inaccurate and only suitable for sufficiently large vessels. There are also ultrasound-based invasive measuring probes, which have to be applied from the exterior onto the blood vessel to be examined, i.e. require an open surgical intervention, and are hence often not practicable.
Non-invasive possibilities include blood-flow measurements using magnetic resonance imaging (MRI) technology, for example, based on phase-contrast MRI. Computed tomography scanning also enables flow determinations in the context of perfusion imaging to some extent. However, these approaches are generally not suitable for interventional techniques, i.e. while a patient is being treated in a catheter laboratory.
There are also some non-invasive techniques based on ultrasound, for example Doppler ultrasound, which, although they can be used in interventional procedures, are relatively imprecise and also require a good acoustic window, which, in particular in the case of intracranial vessels is frequently difficult.